Does anybody know what the bias requirement is for the differential input ports on the RF-Inputs of the LMS7002M ?
The LimeSDR default circuit has them all DC blocked (is this necessary?), but the optimized broadband HF matching network by Danny Webster has it DC grounded. ( https://myriadrf.org/blog/optimising-limesdr-matching-hf/ ). I can’t seem to find a statement in the LMS7002M datasheet that declares this.
Also, the schematic representation for the T3 & T5 input transformers show a Mini-Circuits TC1-1-13MA+ part. The data sheet for this part shows that it is not center-tapped as shown on the LimeSDR schematic. In addition, it is more of a 1:1 balun arrangement. Pin 6 and 4 are one winding and 1 and 3 are the other. If this is true, the ground on pin 4 is carried through (DC wise) to the “rfgn_l_REF_1” pin if using Danny’s circuit. The other differential input is DC connected through the 82 Ohm resistor between the input pins.